This invention relates to a method of displaying monochromatic image on a color image display apparatus such as a color monitor and an image display apparatus for implementing the method. More specifically, the invention relates to a method by which the so-called xe2x80x9cblue basedxe2x80x9d monochromatic films used in the medical field can be displayed in a format (characteristics) suitable for diagnostic purposes. The invention also relates to an image display apparatus for implementing the method.
The diagnostic images taken with medical diagnostic apparatus such as X-ray diagnostic apparatus, MRI (magnetic resonance imaging) apparatus and various types of CT (computed tomographic) apparatus are usually recorded on light-transmitting image recording films such as X-ray films and light-sensitive materials in film form and thereafter reproduced as light-transmissive images. The films showing the reproduced diagnostic images are set on a viewing device called a light fox (xe2x80x9cSchaukastenxe2x80x9d) or a film viewer and illuminated with backlight so that the images are viewed for diagnosis.
Conventionally, apparatus for medical diagnosis and instrumentation have a CRT (cathode-ray tube) display or LCD (liquid-crystal display) connected as a monitor for viewing the images taken and measured with such apparatus. Diagnosis is performed on the basis of the image output to the monitor or the diagnostic images yet to be output on films are checked, adjusted or otherwise processed on the monitor.
The images taken with the medical diagnostic apparatus or those taken and measured with the apparatus for medical diagnosis and instrumentation are often reproduced on so-called xe2x80x9cblue basedxe2x80x9d monochromatic films. The gradation resolution of the reproduced images is typically in 10 bits (providing 1024 gradations).
Two problems are posed here. The first problem is associated with the fact that blue-based monochromatic films are used for image reproduction whereas the monitor screen is white-based. The doctor has to examine both types of images but due to limitations of the human visual sense, it is not easy to switch from one type of image to the other by intuition. To a doctor who has become accustomed to looking at one type of image, the other type is felt difficult to see.
The second problem concerns the fact that CRTs usually display images at a gradation resolution of 8 bits and LCDs usually display images at a gradation resolution of 6 bits, sometimes in 8 bits if they are of the latest high-performance model. Thus, whichever of the monitors in current use display images with image data having a lower gradation resolution than the image data that has been output after image taking and measurement with the apparatus for medical diagnosis and instrumentation, that is to say, so-called xe2x80x9cimage data that cancellation of significant bits has occurredxe2x80x9d.
Therefore, this xe2x80x9ccancellation of significant bits of the image dataxe2x80x9d occasionally causes a kind of noise called xe2x80x9cartefactsxe2x80x9d in contour lines which are commonly called pseudo-contours. Such noise will reduce or spoil the reliability of diagnoses and must be eliminated from medical diagnostic images.
To deal with this second problem, it has been proposed to use frame rate control (FRC) display. In this technique, 10-bit image data may be divided by four to give four frames of 8-bit image data which are displayed consecutively to represent a 10-bit gradation in 8 bits. However, this approach suffers from the problem of flicker in the image for the very reason that FRC is performed.
In order to eliminate flicker, the frame frequency in FRC display has to be increased to permit high enough display switching. In practice, however, the driver IC for the monitor and the monitor itself are limited in response speed. This problem presents considerable difficulty in medical diagnostic applications where an increased number of pixels are used with a view to providing higher image quality by representation of a high-definition image such as QSXGA (2560xc3x972048 pixels).
The present invention has been accomplished under these circumstances and has as an object providing a method of displaying a monochromatic image on a color monitor, by which the so-called xe2x80x9cblue basedxe2x80x9d monochromatic films used in the medical field can be displayed in a format (characteristics) suitable for diagnostic purposes.
Another object of the invention is to provide an image display apparatus that is suitable for implementing the method.
In order to attain the object described above, the present invention provides a method of displaying a monochromatic image on a color monitor, comprising the steps of: displaying the monochromatic image on a color display device with red, green and blue cells as a unit pixel, wherein all density regions of the monochromatic image to be displayed are provided with bluish tints.
In the method of displaying the monochromatic image on the color monitor of the present invention, a higher luminance area of the monochromatic image to be displayed is preferably provided with the more bluish tint.
In the method of the present invention, image data for the monochromatic image is preferably output for display after it is allotted to red, green and blue data to satisfy following relationships:
R data=kRxc2x7B data(0 less than kR less than 1)
G data=kGxc2x7B data(0 less than kG less than 1),
where symbols R, G and B denote red, green and blue, respectively and symbols kR and kG denote allotment ratios for R and G data to B data, respectively.
In the method of the present invention, the above-described allotment ratios kR and kG may particularly satisfy a following relationship: kR=kG=k (0 less than k less than 1), where symbols k denotes an allotment ratio to B data.
Namely, if R data≈ G data less than B data, the monochromatic image to be displayed can be provided with the bluish tints or blue shades over all density regions.
In the method of the present invention, a color space for a color to be represented that has been allotted to the R, G and B data is preferably represented by coordinates (x,y) on a CIE chromaticity diagram and located within a region bounded by coordinates (0.174, 0.0), (0.4, 0.4) and (xcex1, 0.4), where xcex1 is an x-coordinate of a point at which a spectrum locus crosses a straight line that is parallel to an x-axis and which intercepts a y-axis at 0.4.
In the method of the present invention, each of the allotted R, G and B data is subdivided into data for a plurality of frame-rate-control frames by a mask rounding dispersion treatment and the R, G and B data are independently driven by frame-rate-control using the data subdivided to the individual frames.
In the method of the present invention, a liquid-crystal panel is used as the color display device.
The present invention can be actualized as an image display apparatus implementing the method descried above.
That is to say, the present invention can be actualized as an image display apparatus, comprising a color display device using red, green and blue cells as a unit pixel and a data allotting unit by which image data for a monochromatic image to be displayed on the color display device is output for display after it is allotted to red, green and blue data to satisfy following relationships:
R data=kRxc2x7B data(0 less than kR less than 1)
G data=kGxc2x7B data(0 less than kG less than 1),
where symbols R ,G and B denote red, green and blue, respectively and symbols kR and kG denote allotment ratios for R and G data to B data, respectively, wherein the image data for the monochromatic image allotted by the data allotting unit is output as the R, G and B data for display on the color display device.
In the image display apparatus of the present invention, the above-described allotment ratios kR and kG may particularly satisfy a following relationship:
kR=kG=k(0 less than k less than 1).
The R, G and B data may satisfy a following relationship:
R dataxc2x7G data less than B data.
In the image display apparatus of the present invention, the data allotting unit allots the data in such a way that a color space for a color that has been allotted to the R, G and B data is represented by coordinates (x,y) on a CIE chromaticity diagram and located within a region bounded by coordinates (0.174, 0.0), (0.4, 0.4) and (xcex1, 0.4), where xcex1 is an x-coordinate of a point at which a spectrum locus crosses a straight line that is parallel to an x-axis and which intercepts a y-axis at 0.4.
It is preferable that the image display apparatus of the present invention further comprises a drive processing unit by which each of the allotted R, G and B data is subdivided into data for a plurality of frame-rate-control frames by a mask rounding dispersion treatment and the R, G and B data are independently driven by frame-rate-control using the data subdivided to the individual frames.
In the image display apparatus of the present invention, a liquid-crystal panel is used as the color display device.